This is according to Bloomberg News, based on information from an unnamed US official. The data may have been backed up on another machine. Peter Toren, a former computer crimes prosecutor for the Justice Department, says Clinton didn’t use a private server “because it was convenient for her. There’s a ton of email services that are available that are actually quite secure, easy to use, and you can use them on every device.” (Bloomberg News, 8/13/2015)

Security expert Matt Devost similarly comments that when it comes to a private server like Clinton’s, “You erase it and everything’s gone,” while commercial email services like Gmail and Yahoo Mail retain copies even after users erase them from their inboxes, which could be why Clinton didn’t use them for her email account. (Bloomberg News, 3/4/2015)

However, many of Clinton’s top aides did use commercial email services like Gmail and Yahoo Mail, and the FBI could find copies of some of Clinton’s emails by asking those companies to check their back-up copies. (Bloomberg News, 8/13/2015)